The invention relates to a compression-resistant heating frame, which more particularly comprises an upper plate and a lower plate which are secured to each other.
A heating frame comprising an upper plate and a lower plate which are secured to each other is known from document CH 328013 published on 15th Apr. 1958. The frame comprises electrical heating means which are disposed between the two plates, as well as bars made of wood or of plastics material, which are disposed on both sides of the heating means, and are interposed between the upper plate and the lower plate. The resistance to compression of this frame is assured mainly by the means for securing the two plates to each other. The bars which are made of wood or of plastics material reinforce this resistance, but by transmitting all the compression forces to the heating means between which they are interposed.
A heating frame which provides improved resistance to compression is known from document EP-A-2 639 005 published on 15th Nov. 1988. According to this document, the lower plate of the frame comprises receptacles to receive the heating means, which in this case consist of electrical resistors. The receptacles are separated from one another by excess thicknesses of the lower plate, such that the electrical resistors are protected against any deformation when the frame is subjected to a force which compresses the upper and lower plates against each other. A frame of a similar type is also known from document FR 822661 published on 4th Jun. 1937. The heating elements are disposed between the upper and lower plates of the frame, and are protected against deformation by strips which maintain a space between the two plates in which the electrical resistors are disposed.
Although the last two frames described protect the heating means efficiently during compression, they nevertheless have the disadvantage of poor regularity of heating in relation to the size of the upper plate or of the lower plate. In fact, while protecting the electrical resistors against deformation, the alternation of the electrical resistors and the mechanical means, excess thicknesses or strips, creates periodic variation of the temperature of the upper and lower plates of the frame. The temperature is higher in the location of an electrical resistor, and lower in the location of the mechanical means for protection against deformation.